1. Field of the Invention
This invention relates to improvements in flexible, resilient, polyurethane foams, and in particular to improvements in the characteristics of such foams when subjected to fire. The primary objective of the invention is to provide polyurethane foams having significantly enhanced resistance to combustion even when they are exposed to an intense ignition source. Flexible resilient polyurethane foams are made by the reaction of polyols and organic polyisocyanates in the presence of one or more blowing agents, one or more surfactants, and one or more catalysts. The foams find a variety of uses, such as carpet underlay, textile innerlining, mattresses, pillows, furniture padding, cushions, automobile crash pads, and insulation. Unless formulated with special additives, polyurethane foams burn readily when ignited. It is known in the art to add various flame retardant chemicals to polyurethane foam-forming reaction mixtures, in particular to add halogenated esters of phosphorus. This has resulted in some improvement in the flammability properties, the extent of burning after ignition by a low intensity source being reduced and the foams may even be made self-extinguishing to some degree in small scale laboratory tests; but while combustion does occur the foam melts and may drip flaming embers which may ignite other flammable materials in the vicinity and thus cause the fire to spread. Such so-called "self-extinguishing" foams are generally not resistant to ignition by anything other than a low-intensity ignition source. In order to overcome this problem other additives have been added to polyurethane foam-forming reaction mixtures to render the finished foams intumescent, or capable of producing a char, once having been ignited. Such foams are less prone to the development of flaming, dripping, embers during combustion, and produce a char which can act as a thermal insulating barrier and thus slow or prevent the spread of the fire.
2. Description of the Prior Art
In U.S. Pat. No. 3,681,273 the use of a mixture of a nitrogen and phosphorus containing compound such as monoammonium phosphate, melamine phosphate, or urea phosphate, and an N-alkylol substituted polyalkylene polyamine as an additive to conventional flexible polyurethane foam reaction mixtures is disclosed. The resultant foams are flame-retardant, intumescent, and non-burning.
U.S. Pat. No. 3,803,063 discloses a flexible polyurethane foam reaction mixture containing an additive comprising a nitrogen and phosphorus containing compound such as monoammonium phosphate or an ammonium phosphate and a polycondensate of polymerized unsaturated fatty acids with aliphatic amines.
U.S. Pat. No. 3,897,372 discloses hydrophilic polyurethane foams having flame retardancy and reduced smoke density, prepared by reacting a resin prepolymer, water, alumina hydrate, boric acid, and a melamine derivative. Optionally, the reaction mixture can also contain silica.
In U.S. Pat. No. 4,139,501, Rudner, Noone and Pauly disclose flexible polyurethane foams having reduced tendency to form burning embers when ignited and burned, produced by incorporating into the foam-forming reaction mixture a melamine derivative wherein one or more hydrogen atoms have been replaced by hydroxymethyl and/or lower alkoxymethyl groups. Alternatively, a halogenated phosphorus ester can also be included in the reaction mixture.
U.S. Pat. No. 4,143,029 discloses dripless, fire-retarded polyurethane elastomers comprising a blend of an elastomer with a hexaalkoxymethylmelamine, a trihydrocarbylcarbonylmelamine, and an aromatic bismaleimide or aromatic bismaleimide generator.
U.S. Pat. No. 4,162,276 discloses non-dripping, self-extinguishing, polyurethane elastomers comprising a blend of an elastomer with a hexaalkoxymethylmelamine, an organic halogen-containing compound such as a chlorinated paraffin, and a P-substituted phosphocyclopentane 1-oxide.
U.S. Pat. No. 4,197,373 discloses polyether polyurethane foams prepared from conventional foam-forming reaction mixtures containing as a flame retardant a melamine derivative having a 2,2,2-trichloromethyl group, such as N,N'-bis(1-hydroxy-2,2,2-trichloroethyl)melamine.